Method of drying lumber and a dry kiln for carrying the method into effect



6, 1960 A. s. MCRCH METHOD OF DRYING LUMBER AND A DRY KILN FOR CARRYING THE METHOD INTO EFFECT Filed Dec.

INVENTOR.

MGR

gm Pm W q- F mm \N channel.

METHGD F DRYING LUMBER AND A DRY KILN FOR CARRYING THE METHOD INTO EFFECT Arne Soren Miirch, Kyrkogatan 12, Sundsvali, Sweden Filed Dec. 19, 1955, Ser. No. 554,031

2 Claims. (Cl. 34-225) The present invention refers to drying of lumber and dry kilns operating with longitudinal circulation, i.e. to progressive dry kilns consisting, in principle, of a channel, through which the lumber is advanced in one direction longitudinally of the kiln, while hot air is being conveyed in the opposite direction therethrough. Kilns with longitudinal circulation have been constructed with the lumber piled in the longitudinal direction of the kiln or with the lumber piled in the transverse direction thereof. The invention refers, above all, to drying of lumber, the longitudinal direction of which coincides with the transverse direction of the kiln channel during the transport of the lumber therethrough. In other words,- the invention primarily refers to dry kilns operating with longitudinal circulation With the lumber piled in the transverse direction, but is also applicable to dry kilns with longitudinally piled lumber.

It is known in connection with lumber kilns with-socalled transverse circulation to divide the drying process over different controllable sections, so that the drying air is adapted at different points of the drying channel with respect to the quantity and/or temperature thereof according to the percentage of moisture in the lumber in difierent parts of the kiln channel. In these kilns, wherein the air in passing from one end of the channel to the other attains a helicoidal movement, a relatively complicated machine plant with many fans and long pipe conduits is required. Furthermore, it is known in channel kilns to take air to different sections from the external air into separate heating chambers, from which the heated air is introduced in a controllable quantity into the kiln channel.

The present invention relates to a method rendering an effective drying possible in different parts of the kiln channel at a low power and heat consumption with the use of simpler means than those required in kilns with a transverse circulation. The invention aims particularly at an attainment of a distribution as favourable as possible of the drying air in the kiln channel, so that a uniform drying adapted to the moisture percentage of the lumber will be obtained in different parts of the In this method the temperature of the circulating hot air is adapted in known manner, when entering at diiferent points of the kiln channel, with respect to the quantity and/or temperature of the air according to the moisture percentage of the lumber in the various parts of the kiln channel. Furthermore, the whole quantity of consumed wet air is substantially carried off at that end of the kiln channel where the lumher to be dried is introduced, that is to say, at the intake end of the channel. The distinguishing feature of the invention resides, above all, in that the lumber to be advanced in the channel is piled on a conveying contrivance in successive batches with intervening spaces therebetween, the positions of the spaces being adapted with respect to the positions of entrance openings for hot drying air from a common air intake passage so that the drying air will flow into said spaces between the lumber batches in order then to be conveyed through the latter in the longitudinal direction of the kiln channel.

Hot air from the openings is preferably introduced at the same time into some of the intervening spaces between the lumber batches, the distances between the various spaces being so adapted relatively to the distances between the air intake openings that a plurality of spaces will be located at the same time in register with one of said openings. It is possible to elfect the advancement of the lumber so that the space between an arbitrary pair of consecutive lumber batches will be located successively in a position for every air intake opening. This ensures a proper inflow of air and an effective drying of every batch.

A lumber dry kiln suitable for use in carrying said method into effect broadly consists of a kiln channel with conveying means for the advancement of generally transversely piled lumber in batches with intervening spaces between the latter from one end of the kiln chan nel, the intake end, to the opposite end thereof, the outtake end, and the invention is primarily distinguished by the fact that said channel is provided with intake openings for hot air at points along the length of the channel adapted to the distance between said intervening spaces, and that said channel is at the intake end of a section intended for substantially the whole quantity of consumed wet air, so that the air will flow into the spaces between the batches and through the latter in the longitudinal direction of the channel, controlling means and preferably also heating elements being provided to adapt the air velocity and the air temperature in such manner that a suitable velocity and temperature of the air flowing through the lumber batches will be obtained for the corresponding parts of the kiln channel.

Further features of the invention and advantages in connection therewith will appear from the following description of a form of embodiment of a lumber dry kiln illustrated in the drawing, by means of which the method may be carried into effect. Fig. 1 shows a vertical longitudinal section and Fig. 2 is a cross section of the kiln taken along line 2-2 of Fig. 1. Fig. 3 is a detailed sectional View taken along line 33 of Fig. 2 and Fig. 4 is a detailed view of the transporting track and roller means of Fig. 2.

In the illustrated construction, the kiln is provided with two elongated chambers or kiln channels l, 1 running in parallel to each other, but a greater number of such channels, for instance four of them, may also be provided. The processes in the kiln channels and the constructions of the latter being the same, it will thus be sufficient to describe the kiln as if it were provided with one single channel. The lumber is intended to be introduced into the one end 3 of the channel 1 adapted to be closed by a door 2, and is taken out through the other channel end which is provided with an opening 4 and a door 5. Extending above the roof 6 of the channel 1 are one or more longitudinally running air distributing passages 7 along the whole or substantially the whole length of the kiln. The air distributing passage 7 is defined at the top by a horizontal wall 9, and provided above the latter is a transversely extending chamber 10 equipped with an inlet 11 for fresh air. The wall 9 has openings 12, 14 to the air distributing passage provided therein, and the flow of freshair through these openings may be controlled by means of a damper 15 or the like. At the intake end, the roof of the kiln channel is provided with an opening 16 forming an outlet for the moist air escaping from 'the kiln channel.

ing passage 7 and in part through an opening 17 in the wall 9 to an outlet chamber 18 and thence through an i outlet 19 into the atmosphere. The opening 17 may be controlled by means of a damper 20. The path of the air is marked with arrows 21 and that of the lumber with arrows 22.

The roof 6 of the kiln channel is provided with a number of openings 23 provided behind one another in the longitudinal direction of the channel, through which openings air is introduced into the kiln channel from the air distributing passage. In the construction shown, there are provided six such openings behind one another, but a greater or smaller number of openings may also be provided. The air is propelled through the air distributing passages by means of one or more fans 24 preferably located, as in the construction shown, before all openings 23, counted in the direction of the air flow. At each opening 23, and preferably immediately in front of the same, there is provided a heating element 25 consisting, for instance, of pipes extending in the transverse direction of the channel, said pipes having a suitable heating medium, such as steam, flowing therethrough. The openings 23 may be provided with controllable dampers 23' or the like, so that the quantity of air flowing in through each opening may be controlled as required. The heating elements may also be controllable with respect to their yield of heat.

The lumber is arranged in piles or batches on a conveyor, by means of which it is fed through the channel 1 from one end to the other thereof. In the construction shown, there are fourteen lumber batches 26 behind one another in the kiln channel. Intervening spaces 27 are provided between the lumber batches. The lumber of each batch extends with its longitudinal direction in the transverse direction of the channel. The conveying contrivance consists of trucks with longitudinally extending beams 28 and trolleys 29 on rails 30. As will be seen from Figs. 3 and 4, boards 31 intended for the drying process are placed transversely over the beams 23 of the trucks, distance members or so -called bed laths 32 being provided between the boards, such members extending in parallel to the beams 28.

Said layers or boards 33 also extend transversely over the beams. Then follows another layer of bed laths and so forth throughout the pile or batch up to the roof of the kiln channel.

The conveying contrivance is adapted to carry lumaer batches of such dimensions in the longitudinal direction of the kiln channel and with so large spaces between the batches that a plurality of the spaces will at the same time be in a position for some one of the air intake openings. In the position shown in Fig. 1, every second space 27 is in register with an air intake opening 23'. It is possible, however, to arrange batches of a greater or smaller length, for instance in such manner that a space will be located in register with each opening 23-. The length of the truck beams 28 is preferably selected so that the combined length of the beams equals to or is greater than the length of the kiln channel, the ends of consecutive trucks then abutting each other, so that all batches may be moved as a unit by a driving means operative at the intake end. The advancement preferably takes place in a stepwise fashion with approximately the length of a batch in each step. Hereby the space between an arbitrary pair of consecutive lumber batches will, during the transport through the kiln channel, be successively adjusted in a position in register with every air intake opening. Each batch will thus have hot air supplied to the same directly from each air intake opening. Continuous feeding is also conceivable, however. Optionally, screens may be provided in spaces for the conveyance of the air into the lumber batches in a suitable manner. When two lumber batches, such as 26a, 26b, are in that portion of the kiln channel which is located between two successive air intake openings 23, a screen 34 may thus be arranged crosswise through the kiln channel underneath the second batch 26b counted in the direction of the air flow, beind he intervening space v2 7, so that air flowing ahead at the bottom of the channel is directed upwardly by the screen in said space 27 and is permitted to flow therefrom into the second batch 26b. This procedure may also be applied in connection with more than two batches behind one another between two successive air intake openmgs.

The mode of operation of the lumber dry kiln described is broadly as follows:

Lumber that has been piled in the manner set forth on the roller way commencing in front of the intake end of the kiln introduced into the kiln channel so as to fill the latter with lumber batches from. the intake end to the outtake end of the kiln.

Prior to being introduced into the kiln channel proper, any lumber may be subjected to a steam and heat treatment so as to increase the temperature of the lumber. When the kiln channel is filled with lumber, as shown in Fig. 1, air will be propelled by means of the fans 24 through the distributing passage 7. This air consists of dry fresh air, which is admitted in a controllable quantity through the openings 12, 14, and of wet return air coming from the air outlet 16 of the kiln channel. The temperature of the mingled air is increased successively, according as the air flows past the various heating elements 25 The air may thus be controlled so as to be the hottest at the termination of the air distributing passage, that is to say at the 'outake end of the kiln channel, where the lumber is the driest. Inasmuch as a heating element is arranged in front of every intake opening 23 to the kiln channel, the air supplied to this channel through each opening may have that temperature imparted thereto which is suitable for the lumber to which the air is supplied from the opening in consideration. The quantity of air, and thus also the air velocity in the various parts of the kiln channel, may be controlled by the dampers 23' to suitable values, i.e. generally to a lower velocity, for instance to approximately 1 meter per second or more at the end of the kiln channel and to 23 meters per second or more at the commencement of the same. The air entering through the openings 23 in the kiln channel passes through the lumber batches located thereat, so that the lumber is dried. The air then generally flows in the transverse direction of the lumber. By reason of the intervening spaces 27 it will be possible for the air to how down to the lowermost layers in the batch, the air being then also admitted in part underneath the same, so that an eifective and uniform drying of the whole batch is attained. The screens also aid to the attainment of this result, inasmuch as the screens force the air upwardly or downwardly through spaces not located in register with an air intake opening.

The invention is not limited to the embodiment shown and described. As an example of deviations from said embodiment might be mentioned that the drying principle described may also be applied in cases where the lumber is piled in the longitudinal direction of the kiln channel, although the space in the latter cannot then be utilized in the same eifective manner as with transversely piled lumber; this depending on the fact that the boards will then have to be arranged with lateral spaces between them for the air flowing in the longitudinal direction of the channel and cannot be laid edge to edge onto each other, as is the case in connection with transverse piling.

Instead of providing heating elements at each opening 23 one may arrange a common element immediately behind the fans, said element then heating the whole quantity of air. Possibly, one further heating element may be located substantially at the middle of the passage 2 or, generally, above a place in the drying passage where the fibre saturation point of the Wood has been reached. A control of the temperature of the air behind the various openings 23 may then 'be effected by adjusting the dampers 23' to admit the passage of different amounts of air.

Although the kiln has been described hereinbefore in the form of a progresive kiln, it is possible within the scope of the inventionto modify the same into a stationary kiln, that is to say into a kiln wherein the whole channel is filled at once with green lumber for drying.

In addition to a uniform and economical drying of the lumber, the invention results in that the space of the kiln channel can be utilized in the best possible manner. This is intimately bound up with the arrangement of the lumber crosswise in the channel and with the conveying contn'vance suitable therefor. In connection therewith low establishment costs and low transmision losses will be obtained. The mechanical equipment becomes simpler and less expensive than in previous kilns operating with a longitudinal circulation and also in comparison to a kiln with the use of transverse circulation, which is more expensive in said respects. The control members will be fewer and the attendance simpler.

What I claim is:

1. A hot air kiln for drying lumber comprising a kiln housing having a horizontal upper wall and vertical side and end walls, a horizontal lumber channel roof in said housing below and spaced from said housing upper wall dividing said housing into a horizontal lumber drying channel below said channel roof and a horizontal air distributing passage above said channel roof, one end wall of said kiln housing having a closable lumber inlet opening at one end of said :lumber drying channel and the other end wall of said kiln housing having a closable lumber outlet opening at the other end of said lumber drying channel, means in said drying channel for transporting horizontally-spaced stacks of lumber through said drying channel from said lumber inlet opening to said lumber outlet opening, means in the housing top wall adjacent the lumber inlet end of said housing for introducing atmospheric air into said air distributing passage, fan means for propelling the atmospheric air from said introducing means longitudinally of said air passage toward the lumber outlet end of said housing, a plurality of heating elements longitudinally spaced in said air distributing passage for heating to progressively higher temperatures the air flowing therein, said lumber channel roof having a plurality of longitudinally-spaced openings therein for introducing drying air streams of progressively increasing temperature from said air passage into said lumber drying channel, said housing horizontal upper wall having a moisture-laden-air outlet intermediate said atmospheric air inlet means and the lumber inlet end wall of said housing, said lumber channel roof having a moisture-laden-air return opening therein adjacent the lumber inlet end wall of said housing through which passes the moisture-laden air flowing longitudinally through said lumber drying channel from the lumber outlet end toward the lumber inlet end thereof, and damper means in said moisture-laden-air outlet for controlling the proportion of moisture-laden air which is emitted through said outlet and the proportion of moisture-laden air which is recirculated longitudinally through said air distributing passage toward the lumber outlet end of said housing.

2. A lumber drying kiln as defined in claim 1 and further including damper means in said lumber channel roof openings for adjustably controlling the quantities of heated air passing through the various openings. V 

